Geochemical and Multi-Isotope Tracing the Origin and Modification of Oilfield Waters from Jiuquan Basin, Northwestern China
Abstract
The geochemistry of oilfield water contains valuable information that can be used to reconstruct the origin and migration of the oilfield water and potentially also the co-produced oil. Here we evaluate the origin and migration of oilfield waters from four major oilfields of the Jiuquan Basin in northwestern China, which is one of the richest oil basins with potential tight oil exploration in China. We used major and trace elements, coupled with isotope tracers including oxygen and hydrogen, carbon in dissolved inorganic carbon, boron, and strontium isotopes. We show that the original water was generated in the Lower Cretaceous Xiagou Formation in Qingxi Basin through blending deep and highly saline water, evolved from relicts of evaporated seawater, and geothermal water that was generated as part of the formation of the Xiagou Formation. The distinctive geothermal fingerprint was detected also in the adjacent Yaerxia oilfield water, indicating eastward migration of the original geothermal water, combined with several diagenetic modifications including base-exchange reactions and mobilization of Ca and Sr from the host rocks, as well as retention of B and Li through adsorption processes. Further migration of the oilfield water from Yaerxia Basin eastward to the Laojunmiao and Shiyougou basins caused further diagenetic modification with base-exchange and adsorption reactions, as well as sulfate reduction processes that further modified the original geothermal composition. We show that the Laojunmiao oilfield water was later diluted with meteoric water that caused large reduction in the salinity and triggered reverse base-exchange reactions and mobilization of Na and B from clay minerals, as well as biodegradation that resulted in 13C-enriched bicarbonate. The progressively depletion of B and Li and the enrichment of 11B in oilfield waters along with the reconstructed eastward migration enables the distinction between the boron-rich original oilfield water associated with kerogen maturation relative to secondary reactions associated with the transport of the oilfield water. Overall, this study offers novel geochemical tools for reconstructing the origin and geochemical evolution of the oilfield water in Jiuquan Basin and coupling it with the migration pathways of crude oil.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH062.0005V
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1878 Water/energy interactions;
- HYDROLOGY;
- 1895 Instruments and techniques: monitoring;
- HYDROLOGY